Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $165.67   8.201%   $179.2566   $179.26   $179.25   $179.30  
  Purchase #2 $12.84   4.771%   $13.4526   $13.45   $13.45   $13.50  
  Purchase #3 $85.48   3.351%   $88.3444   $88.34   $88.35   $88.30  
  Purchase #4 $214.37   11.807%   $239.6807   $239.68   $239.70   $239.70  
  Purchase #5 $216.94   11.511%   $241.912   $241.91   $241.90   $241.90  
  Purchase #6 $92.60   11.210%   $102.9805   $102.98   $103.00   $103.00  
  Purchase #7 $176.42   13.319%   $199.9174   $199.92   $199.90   $199.90  
  7 purchase totals = $964.32       $1,065.5442   $1,065.54   $1,065.55   $1,065.60